The disclosure relates generally to methods for manufacturing ceramic materials and more particularly to methods of reducing shrinkage in shaped ceramic articles by adjusting the top soak temperature during firing.
Ceramic products of a honeycomb shape have been made by preparing a ceramic green body through mixing of ceramic materials with water and various carbonaceous materials (including extrusion and forming aids) to form a plasticized batch, forming the body into a honeycomb-shaped green body through extrusion of the plasticized batch, and finally firing the honeycomb-shaped ceramic green body in a firing furnace or kiln.
An important factor in the manufacture of honeycomb shaped ceramic articles is minimizing the variability in the shrinkage (or growth) of the ceramic articles during firing, particularly as a result of the sintering process. Product specifications require certain ceramic articles, such as diesel particulate filters (DPFs), to meet increasingly robust specifications with regard to shrinkage (or growth) variability from a target.
Most methods of minimizing the variability in the shrinkage (or growth) of ceramic articles have focused on controlling raw materials (or properties of raw materials) added to the initial batch composition. These methods often include controlling the particle size distribution (PSD) of batch constituents because when there is a significant change in the raw material particle size distribution, there is typically a subsequent high rate of change in shrinkage.
Methods of controlling PSD include measures such as selecting specific ratios of raw material batch constituents with known particle size distributions, calcining or milling raw material batch constituents to a defined particle size distribution, or controlling the rate at which raw material batch constituents are fed through a milling apparatus. However, even when these processes are combined with some sort of feedback control mechanism (e.g., measuring the shrinkage in the fired part and adjusting the raw material feed accordingly) substantial amounts of ware must often be discarded because much material is already in process downstream of raw material feed and mixing at the time it is determined that the raw material feed needs adjustment.